Manure spreaders such as used in agricultural applications are generally of the liquid type and include spray equipment or are intended for use with non-liquid manures and include flail-type spreaders with rotating aprons or movable gates. As used herein, the term "manure" is understood to mean animal waste as well as municipal and industrial waste.
When spreading certain types of manure such as chunks of feed lot manure, the manure tends to bridge over the spreader's conveyor which is typically a rotating auger. This bridging effect prevents the conveyor from continuously engaging and displacing the manure toward and into an expeller for discharge. In effect, a cavity, or hollow space, is formed about the rotating conveyor auger which prevents further engagement of the manure by the conveyor auger. With the spreader typically traveling at a ground speed of 4-6 miles per hour, or approximately six (6) feet per second, and with a discharge pattern of 20-30 feet to the side of the spreader, any interruptions in the auger-expeller feed relationship will result in large gaps in the manure spread pattern. Attempts to break down the self-supporting bridge of hard-packed, dense manure over the conveyor auger have generally involved displacing the conveyor auger vertically. One such approach is disclosed in U.S. Pat. No. 5,085,372, where the conveyor auger is displaced from a lower portion of the V-shaped manure tank in an upward, generally vertical direction to break up the manure forming a bridge over the conveyor auger. While this approach offers an improvement in manure discharge from the spreader tank, the compacted manure on each side of the conveyor auger remains free of the auger and is not discharged from the tank into the expeller. In addition, with the increase in the auger-expeller spacing, the feeding relationship between the auger and expeller may be lost, or at least substantially reduced, to prevent uniform, controlled manure spreading.